It is usual in many cases for environmentally dangerous substances to be disposed in storage receptacles which are sealed with respect to the outside atmosphere, at least for a period of intermediate storage. A typical example of such a substance is uranium hexafluoride (UF.sub.6) which, particularly in the depleted condition, that is to say, after a reduction in its U 235 content, is put into intermediate storage, until being finally eliminated or dumped, in sealed storage receptacles. As it is not always possible reliably to exclude the possibility of damage to such receptacles which are used for transportation and/or intermediate storage, it has been found necessary to make arrangements such that in situations in which the above-mentioned substances are not sufficiently shielded from the ambient atmosphere, for example due to damage to the receptacle or due to other circumstances, it is possible vary rapidly to take steps for restoring the desired situation, that is to say, a situation in which such substances are preserved or stored in a condition of being shielded from the environment. In this connection, it may be desirable, particularly also from the point of view of the necessity to act as rapidly as possible, to firstly provide provisional shielding for the substance, whereupon it is then possible, without the pressure of time, to take the steps which result in the substance being permanently disposed in and shielded in for example an intermediate storage means.